Tilt top anvil with torsion spring

ABSTRACT

A tilt anvil assembly is disclosed which includes a center rod, a head assembly, and a torsion spring configured to pivot the head assembly relative to the center rod. The head assembly has a locking collar defining a locked position preventing pivotal movement of the head assembly, and an unlocked position allowing pivotal movement of the head assembly. The torsion spring selectively engages the locking collar to maintain the locking collar at either the locked or unlocked position.

BACKGROUND

1. Technical Field

The present disclosure relates generally to an anvil assembly which issuitable for use with a circular anastomosis stapler. More specifically,the present disclosure relates to an anvil assembly having a tiltablehead which is suitable for use with a circular anastomosis stapler.

2. Description of Related Art

Circular anastomosis staplers which include an anvil assembly having atiltable anvil head are known in the art. Such tiltable anvil heads havebeen disclosed in U.S. Pat. No. 7,431,191 (“the '191 patent”) and U.S.Publication No. 2008/0230581 to Marczyk (“the '581 Publication”), thecontents of which are incorporated herein by reference in theirentirety. In some known circular anastomosis staplers, a locking collaror a backup plate located within the anvil assembly is positioned toinhibit tilting of the anvil head of the anvil assembly prior to firingof the stapler. Upon firing of the stapler, a knife blade of the staplerengages or becomes embedded into the locking collar, and moves thelocking collar to a position which allows the anvil head to tilt uponretraction of the knife blade from the locking collar. If the lockingcollar sticks to the knife blade upon retraction of the knife blade, thelocking collar may return to its position preventing tilting of theanvil head. Thus, the anvil head will not tilt.

In order to effect tilting of the anvil head upon retraction of theknife blade, both the '191 patent and the '581 Publication disclose aplunger and a plunger spring which engage a post on the anvil head totilt the anvil head. To inhibit the locking collar from sticking to theknife blade and, the '191 patent and the '581 Publication disclose aretainer clip and a pivotal latch assembly, respectively, to engage thelocking collar upon retraction of the knife blade.

Despite recent improvements to circular anastomosis instruments, a needstill exists for an anvil head assembly with a simplified mechanism toeffect tilting of the anvil head and to inhibit the locking collar fromsticking to the knife blade upon retraction of the knife blade.

SUMMARY

The present disclosure features a tilt anvil assembly including atorsion spring for pivoting an anvil between a non-tilted position and afully tilted position.

One aspect of the present disclosure features a tilt anvil assemblywhich includes a center rod, a head assembly, and a torsion spring. Thehead assembly includes a housing, a locking collar, and an anvil platehaving staple deforming pockets. The torsion spring is configured topivot the head assembly relative to the center rod.

The locking collar has a locked position preventing pivotal movement ofthe head assembly, and an unlocked position allowing pivotal movement ofthe head assembly.

In one embodiment, the torsion spring includes a coiled structure and atleast one biasing member extending radially outwardly from the coiledstructure. The at least one biasing member includes a middle memberhaving an arcuate profile.

In some embodiments, the middle member is configured to engage thelocking collar to facilitate holding the locking collar at a lockedposition inhibiting pivotal movement of the head assembly. The middlemember may also be configured to engage the locking collar to maintainthe locking collar at an unlocked position inhibiting proximal movementof the locking collar and allowing pivotal movement of the headassembly.

Another aspect of the present disclosure features a method for pivotingan anvil head assembly of a surgical anvil assembly. The method includesa step of providing an anvil assembly which includes a rod, a headassembly, a locking collar, and a torsion spring. The torsion spring isconfigured to pivot the head assembly relative to the rod. The torsionspring defines a normal configuration and a biased configuration. Themethod further includes a step of tilting the head assembly as thetorsion spring transitions from the biased configuration to the originalconfiguration.

The method may include the steps of locking the head assembly at anon-tilted position via the locking collar, and unlocking the headassembly from the non-tilted position.

The method may also include the steps of firing the stapler to advance aknife blade into the locking collar, moving the locking collar from alocked position inhibiting pivotal movement of the head assembly to anunlocked position allowing pivotal movement of the head assembly.

Further, the method may include the step of maintaining the lockingcollar at the unlocked position while extracting the knife blade fromthe locking collar.

DESCRIPTION OF THE DRAWINGS

Various embodiments of the presently disclosed tilt anvil assembly aredisclosed herein with reference to the drawings wherein:

FIG. 1 is a perspective view of a surgical stapling device including anembodiment of an anvil assembly according to the present disclosure;

FIG. 2 is a front perspective view of the presently disclosed tilt anvilassembly with the anvil head untilted;

FIG. 3 is a rear perspective view of the tilt anvil assembly shown inFIG. 2;

FIG. 4 is a rear perspective view, with parts separated, of the tiltanvil assembly shown in FIG. 2;

FIG. 5 is a perspective view of a torsion spring of the tilt anvilassembly shown in FIG. 4 in its original configuration;

FIG. 6 is a perspective, distal view of a center rod assembly of thetilt anvil assembly of FIG. 4;

FIG. 7 is a cross-sectional view of the tilt anvil assembly taken alongthe line 7-7 of FIG. 3 with the anvil head in a locked, non-tiltedposition;

FIG. 8 is an enlarged view of the distal end of the tilt anvil assemblyof FIG. 7;

FIG. 9 is a cut-away view of the tilt anvil assembly shown in FIG. 2with the anvil head in a locked, non-tilted position;

FIG. 10 is a side cross-sectional view of the tilt anvil assembly takenalong the line 10-10 of FIG. 9;

FIG. 11 is a side cross-sectional view of the tilt anvil assembly shownFIG. 9 with the anvil head in an unlocked, non-tilted position;

FIG. 12 is a side cross-sectional view of the tilt anvil assembly shownin FIG. 7 with the anvil head in an unlocked, non-tilted position;

FIG. 13 is a side cross-sectional view of the tilt anvil assembly shownin FIG. 2 with the anvil head in a fully tilted position;

FIG. 14 is a side perspective view of the anvil assembly shown in FIG.13; and

FIG. 15 is a perspective view of the surgical stapling device of FIG. 1with the anvil head in a fully tilted position.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the presently disclosed anvil assembly will now bedescribed in detail with reference to the drawings in which likereference numerals designate identical or corresponding elements in eachof the several views. Throughout this description, the term “proximal”will refer to the portion of the instrument closest to the operator andthe term “distal” will refer to the portion of the instrument furthestfrom the operator.

FIG. 1 illustrates an embodiment of a surgical stapling deviceconfigured for use with a tilt anvil assembly according to the presentdisclosure. Briefly, surgical stapling device 10 includes a proximalhandle assembly 12, an elongated central body portion 14 including acurved elongated outer tube 14 a, and a distal head portion 16.Alternately, in some surgical procedures, e.g., the treatment ofhemorrhoids, it is desirable to have a substantially straight,shortened, central body portion. The length, shape and/or the diameterof body portion 14 and distal head portion 16 may also be varied to suita particular surgical procedure.

With reference still to FIG. 1, handle assembly 12 includes a stationaryhandle 18, a firing trigger 20, a rotatable approximation knob 22 and anindicator 24. A pivotally mounted trigger lock 26 is fastened to handleassembly 12 and is manually positioned to inhibit inadvertent firing ofstapling device 10. Indicator 24 is positioned on the stationary handle18 and includes indicia, e.g., color coding, alpha-numeric labeling,etc., to identify to a surgeon whether the device is approximated and isready to be fired. Head portion 16 includes an anvil assembly 30 and ashell assembly 31. For a more detailed discussion of surgical stapler10, please refer to the '191 patent.

Referring now to FIGS. 2-17, an embodiment of the present disclosure isshown generally as anvil assembly 30. As illustrated in FIGS. 2-3, theanvil assembly 30 includes a head assembly 112 and a center rod assembly114 which defines an axis “A” along its length. The anvil assembly 30has a non-titled or operative position, at which the head assembly 112is generally perpendicular to the center rod assembly 114. The anvilassembly 30 also has a fully tilted position, at which the head assembly112 is substantially coaxially aligned with respect to the center rodassembly 114 (FIGS. 13 and 14). The head assembly 112 is pivotable withrespect to the center rod assembly 114 between the non-tilted positionand the fully tilted position.

With reference to FIG. 4, the head assembly 112 includes a post 116, ahousing 118, a locking collar 120, and an anvil plate 124. The post 116is centrally positioned through a bore in the housing 118. Alternately,the post 116 may be integrally formed with the housing 118. The anvilplate 124 is supported on the housing 118 in an outer annular recess 128and includes a plurality of pockets 130 for receiving and deformingstaples. At least one tab 124 a extends radially outwardly from theanvil plate 124 and is dimensioned to be received within a cutout 132formed in the housing 118. The tab 124 a and the cutout 132 function toalign the anvil plate 124 within the annular recess 128.

The locking collar 120 includes a central opening 122 which ispositioned about the post 116 within an inner recess 134 of the housing118 between the post 116 and annular recess 128, such that the lockingcollar is slidably mounted about the post 116. The locking collar 120may be formed from metal or other alternate materials.

In one embodiment, as illustrated in FIG. 4, the locking collar 120includes three tabs 138 a, 138 b and 138 c extending inwardly towardsthe central opening 122. The first and second tabs 138 a, 138 b arearranged in a manner such that they are diametrically opposed to eachother along an axis “B”, and the third tab 138 c is placed equidistantfrom both the first and second tabs 138 a, 138 b on an axis “C”perpendicular to the axis “B.” It is also envisioned that the lockingcollar 120 may include any number of tabs extending towards the centralopening 122 arranged in any conceivable manner different from thatdescribed above.

In one embodiment, as seen in FIG. 9, each of the first and second tabs138 a-b has an internal surface 139 a-b, respectively, and each internalsurface 139 a-b has a uniform arcuate, convex cross-sectional profilealong the thickness “T” of the locking collar 120. However, asillustrated in FIGS. 9-10, the third tab 138 c includes a first inclinedinternal wall 139 c forming an acute angle with respect to a lowersurface 120 a of the locking collar 120. In some embodiments, the thirdtab 138 c may also include a second inclined internal wall 139 d betweenthe first inclined internal wall 139 c and the lower surface 120 a andforming an obtuse angle with respect to the lower surface 120 a.However, it is contemplated that the three tabs 138 a-c may define otherconfigurations different from that described above.

With reference to FIG. 4, the post 116 defines a pair of transversethroughbores 136 axially aligned with respect to a pivotal axis “D”,which is parallel to the axis “B” of the locking collar 120. The post116 also defines a transverse slot 137 perpendicular to the pivotal axis“B.” The transverse slot 137 is dimensioned to accommodate the tab 138 cof the locking collar 120 therein. When assembled, the locking collar120 is slidably mounted about the post 116 with the third tab 138 cslidably mounted within the transverse slot 137 of the post 136.

With continued reference to FIG. 4, the center rod assembly 114 includesa center rod 140 and a torsion spring 150 having a throughbore 154defined therein. The center rod 140 includes a first end 142 defining abore 142 a therein dimensioned to releasably engage an anvil retainer115 as shown in FIG. 15 to connect the anvil assembly 30 to the rest ofthe surgical stapling device 10. More detailed discussion of the anvilretainer 115 with which the anvil assembly 30 may be used is disclosedin the '191 patent. The center rod assembly 114 also includes a secondend 144 having a pair of arms 146 which define a cavity 146 atherebetween dimensioned to accommodate the torsion spring 150 and thepost 116 therein. Each arm 146 defines a throughbore 148 therein.

When assembled, the post 116 and the torsion spring 150 are positionedwithin the cavity 146 a of the center rod assembly 114, such that thethroughbores 136 of the post 116, the throughbore 154 of the torsionspring 150 as well as the throughbores 148 of the center rod 140 arecoaxially aligned along the pivotal axis “D,” with a pivot member 162disposed through the throughbores 148, 154 and 136. As a result, thetorsion spring 150 engages both the head assembly 112 and the center rodassembly 114, causing the head assembly 112 to be pivotally secured tothe center rod assembly 114 about the pivotal axis “D.”

FIG. 5 illustrates one embodiment of the torsion spring 150. Asillustrated in FIG. 5, the torsion spring 150 includes a coiledstructure 152 which defines the throughbore 154 therein. The coiledstructure 152 has a first end 152 a and a second end 152 b. The torsionspring 150 also includes two biasing members 156, 158 each extendingradially outwardly from one end of the coiled structure 152. It isenvisioned that in their normal, unbiased configuration, the two biasingmembers 156, 158 appear to intersect each other seen from the side asillustrated in FIGS. 4-5 and define an acute arcuate angle “θ”therebetween. The torsion spring 150 may comprise a deformable, elasticand resilient material. The two biasing members 156, 158 may be biasedunder an application of external force such that the two biasing members156, 158 may extend in diametrically opposite directions as illustratedin FIG. 7. When biased as such, the torsion spring 150 exerts springforce to urge the two biasing members 156, 158 back to their normal,unbiased configuration as in FIGS. 4-5.

It is envisioned when the two biasing members 156, 158 are biased toextend diametrically opposite from each other, the head assembly 112 isin a non-tilted, operative position, whereas when the two biasingmembers 156, 158 are in their normal configuration, the head assembly112 is in a fully tilted position. For instance, when the head assembly112 is in a non-tilted, operative position as illustrated in FIG. 7, thetwo biasing members 156, 158 extend in diametrically oppositedirections, and the torsion spring 150 exerts spring force to resume thetwo biasing members 156, 158 to their normal, configuration asillustrated in FIG. 5, which, in turn, urges the head assembly 112 topivot about the rod assembly 114 about the pivotal axis “D”. When thetorsion spring 150 returns to their normal, unbiased configuration, thehead assembly 112 is in a fully tilted position relative to the centerrod assembly 114 as illustrated in FIGS. 13-14. Accordingly, the anglebetween the two biasing members in their normal configuration controlthe amount of rotation, or the extent of tilting of the head assembly112 relative to the center rod assembly 114 from the non-tilted positionto the fully tilted position.

The torsion spring 150 may exhibit other configurations. In someembodiments, the two biasing members 156, 158 in their normalconfiguration may define angles of any degree therebetween. In otherembodiments, the torsion spring 150 may include only one biasing member156 extending radially outwardly from the coiled structure 152.

With reference to FIGS. 7-8, the torsion spring 150 may be arranged inthe anvil assembly 30 in a manner such that the first biasing member 156of the torsion spring 150 extends distally into the housing assembly112, specifically, in a space defined between the transverse slot 137 ofthe post 116 and the third tab 138 c of the locking collar 120, and thesecond biasing member 158 extends proximally into the cavity 146 a ofthe center rod assembly 114. It is envisioned that the second biasingmember 158 may be securely fixed to an internal surface 146 b of thecavity 146 a by welding, gluing or other fastening mechanisms.

It is envisioned that the locking collar 120 may have two positionsrelative to the center rod assembly 114. In a first, locked position asillustrated in FIGS. 9-10, the center rod assembly 114 engages thelocking collar 120 thereby preventing the head assembly 112 frompivoting about the center rod assembly 114. Specifically, each arm 146the center rod 140 includes a protrusion 149 a extending from a distalsurface 149 b thereof, configured to selectively engage one of the firstand second tabs 138 a-b of the locking collar 120. As seen in FIGS.9-10, when the locking collar is in the first, locked position, eachpair of the protrusions 149 a and the distal surfaces 149 b immediatelyabuts one the first and second tabs 138 a-b of the locking collar 120.It is envisioned that the locking force exerted by the center rodassembly 114 on the locking collar 120 surpasses the spring forceexerted by the torsion spring 150, thereby inhibiting the head assembly112 from pivoting relative to the center rod assembly 114.

In a second, unlocked position as illustrated in FIG. 11, theprotrusions 149 a and distal surfaces 149 b of the center rod assembly114 disengage from the first and second tabs 138 a-b of locking collar120, thereby removing the locking force exerted on the locking collar120, thus allowing the head assembly 112 to pivot about the center rodassembly 114 under the influence of the torsion spring 150.

It is envisioned that firing of the stapling device 10, or advancingsurgical staplers into tissue, may transition the locking collar 120from its locking position to its unlocked position. For instance, asillustrated in FIGS. 9-10, before firing the stapling device 10, thecenter rod assembly 114 secures the head assembly 112 to a pre-firednon-tilted position and limits pivotal movement of the head assembly112.

Upon firing of the stapling device 10, the knife blade (not shown)engages with and becomes embedded into the locking collar 120. The knifeblade moves the locking collar 120 into annular recess 128 of thehousing 118 of the head assembly 112. When such movement occurs, asillustrated in FIG. 11, the first and second tabs 138 a-b of the lockingcollar 120 move distally away and unlocks from protrusions 149 a anddistal surfaces 149 b of the center rod 140, thereby unlocking the headassembly 112 from its non-tilted position.

In one embodiment, the torsion spring 150 may also be configured tofacilitate holding the locking collar 120 in the locked and unlockedpositions. For instance, as illustrated in FIG. 5, at least one of thebiasing members of the torsion spring 150, e.g., the first biasingmember 156 that extends into the housing assembly 112, may include twoside portions 156 a-b each generally exhibiting a straight, elongatedconfiguration and a middle portion 156 c exhibiting an arcuateconfiguration.

The middle portion 156 c is configured to selectively engage the lockingcollar 120 to facilitate holding the locking collar 120 at either thelocked or unlocked position. For instance, as illustrated in FIGS. 7-8,when the locking collar 120 is in the locked position, the third tab 138c formed on the locking collar 120 is disposed immediately proximallywith respect to the middle portion 156 c of the torsion spring 150. Thefirst inclined internal wall 139 c of the third tab 138 c engages theproximal surface 156 d of the middle portion 156 c. As a result, theprotrusion formed by the middle portion 156 c prevents the lockingcollar 120 from moving distally to its unlocked position. Accordingly,the torsion spring 150 facilitates the center rod assembly 114 inholding the locking collar 120 at its locked position, therebyinhibiting unintended activation of the stapling device 10.

As discussed above, upon firing of the stapling device 10, the knifeblade (not shown) engages or become embedded into the locking collar 120and moves the locking collar 120 distally, unlocking the locking collar120 from the center rod assembly 114, which, in turn, causes the lockingcollar 120 to move distally away from the center rod assembly 114. Asillustrated in FIG. 12, during this process, the third tab 138 c of thelocking collar 120 moves distally away from and passes over the middlemember 156 c of the biasing member 156. As a result, the third tab 138 cis situated distally with respect to the middle member 156 c, and thesecond inclined internal wall 139 d of the third tab 138 c engages adistal surface 156 e of the middle portion 156 c. The protrusion formedby the middle portion 156 c now inhibits the locking collar 120 frommoving proximally. As a result, upon extraction of the knife blade fromthe locking collar 120, the middle portion 156 c inhibits proximalmovement of the locking collar 120, thereby maintaining the headassembly 112 in the unlocked position.

When the head assembly 112 is unlocked from its non-tilted position, asillustrated in FIG. 13-15, the torsion spring 150 exerts spring force toreturn the two biasing members 156, 158 to their normal configuration asillustrated in FIG. 5. As illustrated in FIG. 13, while the biasingmember 156 rotates in a counterclockwise direction to resume the normalconfiguration, the biasing member 156 engages the post 116 and urges thehead assembly 112 to tilt about the axis “D.” It is envisioned that whenthe two biasing members 156, 158 of the torsion spring 150 resume theirnormal configuration, the head assembly 112 is fully tilted such thatthe head assembly 122 is substantially in line with the axis “A” of thecenter rod assembly 114 as illustrated in FIGS. 14-15.

It is noted that the head assembly 112 will not immediately tilt uponfiring of the stapling device 10 because, upon firing, the head assembly112 is in an approximated position, i.e., the anvil head assembly 112 isin close alignment with the shell assembly 31 of the stapling device 10.As such, the head assembly 112 will only begin to tilt when the headassembly 112 and the shell assembly 31 of the stapling device 10 arebeing unapproximated as illustrated in FIG. 15.

It will be understood that various modifications may be made to theembodiments disclosed herein. The above description should not beconstrued as limiting, but merely as exemplifications of preferredembodiments. Those skilled in the art will envision other modificationswithin the scope and spirit of the claims appended hereto.

What is claimed is:
 1. A tilt anvil assembly comprising: a center roddefining a longitudinal axis; a head assembly including a housing, alocking collar, and an anvil plate having staple deforming pockets; anda torsion spring configured to pivot the head assembly relative to thecenter rod from a non-pivoted position to a pivoted position; whereinwhen the head assembly is in the non-pivoted position, the lockingcollar is longitudinally movable from a first position where at least aportion of the locking collar is disposed proximally of a portion of thetorsion spring, to a second position where at least a portion of thelocking collar is disposed distally of the portion of the torsionspring.
 2. A tilt anvil assembly according to claim 1, wherein thelocking collar has a locked position preventing pivotal movement of thehead assembly, and an unlocked position allowing pivotal movement of thehead assembly.
 3. A tilt anvil assembly according to claim 1, whereinthe locking collar includes three tabs extending inwardly towards acentral opening of the locking collar, and wherein two of the three tabsare placed diametrically opposed to each other, and a third tab isplaced equidistant from the other two tabs.
 4. A tilt anvil assemblyaccording to claim 1, wherein the torsion spring includes a coiledstructure and at least one biasing member extending radially outwardlyfrom the coiled structure.
 5. A tilt anvil assembly according to claim4, wherein the at least one biasing member of the torsion springincludes two biasing members, and wherein the two biasing members of thetorsion spring have a normal configuration in which the two biasingmembers define an acute angle therebetween.
 6. A tilt anvil assemblyaccording to claim 5, wherein the torsion spring comprises a resilientmaterial such that the two biasing members have a tendency to return totheir normal configuration when biased.
 7. A tilt anvil assemblyaccording to claim 4, wherein the at least one biasing member includes amiddle member having an arcuate profile.
 8. A tilt anvil assemblyaccording to claim 7, wherein the middle member is configured to engagethe locking collar to facilitate holding the locking collar at a lockedposition preventing pivotal movement of the head assembly.
 9. A tiltanvil assembly according to claim 7, wherein the middle member isconfigured to engage the locking collar to maintain the locking collarat an unlocked position preventing proximal movement of the lockingcollar and allowing pivotal movement of the head assembly.
 10. A tiltanvil assembly according to claim 4, further comprising a post disposedin mechanical cooperation with the housing, and wherein the post definesa transverse slot therein to accommodate the at least one biasing memberof the torsion spring.
 11. A tilt anvil assembly according to claim 10,the center rod defines a cavity therein to accommodate the torsionspring and the post of the head assembly.
 12. A tilt anvil assemblyaccording to claim 4, wherein the at least one biasing member of thetorsion spring includes two biasing members.
 13. A tilt anvil assemblyaccording to claim 1, wherein the locking collar has a tab toselectively engage the torsion spring.
 14. A tilt anvil assemblyaccording to claim 13, wherein the tab includes a first inclinedinternal wall and a second inclined internal wall.
 15. A tilt anvilassembly according to claim 1, wherein a portion of the torsion springextends through an opening of the locking collar.
 16. A tilt anvilassembly according to claim 1, wherein the head assembly is preventedfrom pivoting when the locking collar is in the first position, andwherein the head assembly is capable of pivoting when the locking collaris in the second position.
 17. A method for pivoting an anvil headassembly of a surgical anvil assembly comprising: providing an anvilassembly including: a rod; a head assembly; a locking collar; and atorsion spring configured to pivot the head assembly relative to the rodfrom a non-pivoted position to a pivoted position; and while the headassembly is in the non-pivoted position, moving the locking collar froma first position where at least a portion of the locking collar isdisposed proximally of a portion of the torsion spring and where thehead assembly is prevented from pivoting, to a second position where atleast a portion of the locking collar is disposed distally of theportion of the torsion spring and where the head assembly is capable ofpivoting.
 18. The method of claim 17, further comprising distallyadvancing a knife blade into the locking collar to move the lockingcollar distally with respect to the central rod.
 19. The method of claim18, further comprising maintaining the locking collar in an unlockedposition while proximally moving the knife blade with respect to thelocking collar.
 20. A tilt anvil assembly comprising: a center rod; ahead assembly including a housing, a locking collar, and an anvil platehaving staple deforming pockets; and a torsion spring configured topivot the head assembly relative to the center rod, the torsion springincluding a coiled structure and at least one biasing member extendingradially outwardly from the coiled structure.
 21. A tilt anvil assemblyaccording to claim 20, wherein the at least one biasing member of thetorsion spring includes two biasing members, and wherein the two biasingmembers of the torsion spring have a normal configuration in which thetwo biasing members define an acute angle therebetween.
 22. A tilt anvilassembly according to claim 21, wherein the torsion spring comprises aresilient material such that the two biasing members have a tendency toreturn to their normal configuration when biased.
 23. A tilt anvilassembly according to claim 20, wherein the at least one biasing memberincludes a middle member having an arcuate profile.
 24. A tilt anvilassembly according to claim 23, wherein the middle member is configuredto engage the locking collar to facilitate holding the locking collar ata locked position preventing pivotal movement of the head assembly. 25.A tilt anvil assembly according to claim 23, wherein the middle memberis configured to engage the locking collar to maintain the lockingcollar at an unlocked position preventing proximal movement of thelocking collar and allowing pivotal movement of the head assembly.
 26. Atilt anvil assembly according to claim 20, further comprising a postdisposed in mechanical cooperation with the housing, and wherein thepost defines a transverse slot therein to accommodate the at least onebiasing member of the torsion spring.
 27. A tilt anvil assemblyaccording to claim 20, wherein the at least one biasing member of thetorsion spring includes two biasing members.
 28. A tilt anvil assemblyaccording to claim 20, wherein the locking collar includes a tab toselectively engage the torsion spring, and wherein the tab includes afirst inclined internal wall and a second inclined internal wall.